doc bugfix for corner command
loosen requirements for window to be returned from windowUnderPoint

specifically, if AXUIElementCopyElementAtPosition returns an accessibility element that doesn't have the window role or attribute, return it anyway.

for jigish/slate#343. makes windowUnderPoint() work with Emacs 24.3+
Merge pull request #6 from snarfed/master

 loosen requirements for window to be returned from windowUnderPoint